1. Field of the Invention
The present invention generally relates to a plate assembly. More specifically, the invention relates to a plate assembly capable of being widely used as a micro chip or the like (e.g. a capillary electrophoresis chip) which is used in a technical field called the integrated chemistry.
2. Description of the Prior Art
In recent years, there is known a technique called the integrated chemistry for preparing a fine groove having a width and depth of about tens to two hundreds micrometers in a micro chip of a glass or plastic, to use the fine groove as a liquid passage, a reaction vessel or a separation/purification detecting vessel, to integrate a complicated chemical system into the micro chip. According to such an integrated chemistry, a micro chip (Lab-on-chip) having a fine groove capable of being used in various tests is called a total analytical system (μ-TAS) if the use of the micro chip is limited to analytical chemistry, and the micro chip is called a micro reactor if the use of the micro chip is limited to a reaction. When various tests, such as analyses, are carried out, the integrated chemistry has advantages that the time to transport diffusible molecules is short due to its small space and that the heat capacity of a liquid phase is very small. Therefore, the integrated chemistry is noticed in the technical field wherein a micro space is intended to be utilized for carrying out analysis and chemical synthesis. Furthermore, the term “test” means a test carried out by any one or combinations of operations and means, such as analysis, measurement, synthesis, decomposition, mixing, molecular transportation, solvent extraction, solid phase extraction, phase separation, phase combination, molecular uptake, culture, heating and cooling.
In such an integrated chemistry, a capillary electrophoresis chip used in a test in the field of, e.g. biochemistry, has a fine groove or circular recessed portion having a width and depth of 10 to 200 micrometers in the chip of a glass or plastic, to use the fine groove or recessed portion as a liquid passage or reaction vessel to separate and identify a very small amount of vital materials, such as nucleic acids and proteins, and other low molecular materials, and to handle materials having a very small volume of nanoliters to picoliters. Therefore, it is required to precisely form the fine groove.
As methods for forming a fine groove (a hollow portion) in a glass or plastic, there are blow molding and lost-core methods. It is difficult for these methods to precisely form a fine groove having a cross section tens micrometers square. Therefore, there is adopted a method for forming a fine groove in a surface of a glass or plastic plate to bond a lid member (another plate) to the surface of the plate having the fine groove. As methods for bonding two plates, there are generally known ultrasonic welding, vibrating welding, laser beam welding, insert molding (see Japanese Patent Laid-Open No. 11-58467) and adhesion (see Japanese Patent Laid-Open Nos. 2000-246092 and 2000-288381).
However, in the ultrasonic welding and vibrating welding, materials to be bonded to each other are locally melted, so that there is the possibility that a hollow portion having a cross section, e.g. about tens micrometers square, may be deformed. In addition, it is required to use a special equipment to increase costs. Therefore, the ultrasonic welding and vibrating welding can not be adopted.
In the laser welding, it takes a lot of welding time when the shape of the fine groove is complicated, and it is required to use a special equipment, so that there is a problem in that production costs are increased.
In the insert molding disclosed in Japanese Patent Laid-Open No. 11-58468, a plastic plate having a fine groove is previously housed in a cavity of an injection molding die, and a film covering the fine groove is arranged on the surface of the plastic plate. Thereafter, a plastic to be formed as a lid member is injected into the cavity to form a capillary electrophoresis chip. In the insert molding, there are problems in that the shape of the die is complicated and production costs are increased.
In the adhesion, a lid member is fixed to the surface of a plate having a fine groove with an adhesive. If the lid member is simply pasted on the plate, there is some possibility that the adhesive is extruded into the fine groove so that the adhesive entering the fine groove changes the cross section of the fine groove or fills up the fine groove. However, if it is possible to prevent such troubles from being caused, it is possible to efficiently form a capillary electrophoresis chip at low costs without the need of any special equipment.
Therefore, as disclosed in Japanese Patent Laid-Open Nos. 2000-246092 and 2000-288381, there has been developed a technique wherein an energy line curable composition is used as an adhesive to irradiate a part of the adhesive other than that in a fine groove with energy lines to harden the part of the adhesive to wash and remove only the adhesive in the fine groove with a solvent. However, there are problems in that it is difficult to simply carry out such a technique in an actual production field considering productivity and that such a technique requires an expensive equipment.